This invention relates generally to dynamoelectric machines and more particularly to a stator and rotor construction therefor.
Dynamoelectric machines of the type to which the present invention generally relates have a stator including a stator core and windings on the stator core, and a rotor including a rotor core and permanent magnets mounted on the periphery of the rotor core. The rotor core and stator core are typically manufactured by stamping a number of rotor and stator laminations from a ferromagnetic sheet material and stacking the laminations together in respective stacks. Generally, electronically commutated motors require detection of the rotor position in order to commutate the windings on the stator. A Hall device is one common type of sensor used to detect the rotor position. In order for a Hall device to operate, it is necessary for it to be at least partially in radial registration with the permanent magnets inside the motor. The Hall device detects the passing magnetic fields of the permanent magnets indicative of the rotor position and transmits this information to a control in the motor for use in commutating the windings.
However, conventionally the rotor core and permanent magnets mounted on the rotor core have been located entirely within the stator core. A Hall device will not operate properly when located at an axial end of the permanent magnets. The requirement for a minimal air gap between the rotor and the stator in the stator bore rules out placing the sensor between the rotor and stator. Frequently, the rotor core and the permanent magnets mounted thereon are made longer than the stator core so that the permanent magnets are exposed outside the stator core. In this configuration it is possible for a Hall device to extend from a control board to a position in partial radial alignment with the permanent magnets. Unfortunately, making the rotor core longer than the stator core requires that more rotor laminations be punched than stator laminations. There must be a back up die in the manufacturing facility to produce the additional rotor laminations required to form the longer rotor cores. Thus, there is additional manufacturing expense caused by the need for additional machinery as well as the additional material used for the rotor core.
The stator laminations making up the stator core each have slots on an inner diameter of the stator lamination which open into a central opening of the stator lamination. When the stator laminations are stacked together, the slots are aligned with slots of other stator laminations to form elongate stator core slots. Adjacent stator core slots define teeth of the stator core on which the magnet wire forming the stator windings are wound. The magnet wire is received in the slots. To provide additional electrical insulation between the magnet wire and the stator core slot liners are placed into the stator core slots prior to the winding of the magnet wire so that the liners prevent contact of the magnet wire with the stator core.
An example of the slot liner of this type is shown in co-assigned U.S. Pat. No. 5,306,976. The liner has a transverse wall, opposing side walls and flaps extending from edges of the side walls. The flaps overlap so that the slot liner completely encircles the magnet wire in the slots. However, the flaps can be deflected apart by wire being wound on the stator core to permit the wire to enter the slot. The slots are formed with radially opposing inner and outer surfaces to engage the slot liner and hold it in the slot. It is desirable to further increase the spacing between the stator teeth at the end of the slot in order to decrease flux leakage between adjacent teeth.